Requiem for a dream...coke or heroin?

okay so i've seen this movie many many times since i was about 13. i even had it on vhs (which was edited) but i have also seen the unrated version. my question is...are harry and tyrone shooting coke or heroin? i used to believe that they were shooting heroin...but now believe all three of them were coke addicts. because obviously marion is snorting what harry and tyrone are selling...and it has been widely accepted that marion is snorting coke. harry and tyron often talk about getting "a pound of pure" and i think that more-so appliesto cocaine. plus, there is a scene where you can see them cutting the powder on a table. wikipedia says they do heroin...but i think now that they're all doing cocaine. but i could be wrong i suppose.